This invention relates to a primer composition, more specifically to a primer composition which permits providing extremely good adhesion properties between the primer composition and each of a glass plate and an adhesive by previously applying the primer composition to the glass plate, when joining the glass plates is carried out with the adhesive.
Heretofore, as the primers used in causing the glasses to adhere to each other, there are known, for example, organic silicon compounds, i.e. silane coupling agents and their mixtures, which have carbon functional groups such as vinyl groups, amino groups, glycidoxy groups, methacyloxy groups and mercapto groups and in which silicon functional groups such as alkoxy groups, alkoxy-alkoxy groups and acetoxy groups are directly bonded to silicon atoms (e.g., Japanese Provisional Patent Publication No. 65232/1973). Although being excellent in the adhesion properties to the glass, these silane coupling agents are insufficient in an affinity for adhesive layers, depending upon kinds of adhesives. Therefore, they have the problems that a peel-off phenomenon occurs at the interfacial layer between the adhesive layer and the primer layer.
Further, another kind of primer is extensively known in which an epoxy resin and an amino group-containing alkoxysilane are employed together. However, such a primer has the drawback that it can not provide a sufficient adhesive strength, depending upon certain kinds of adhesives.
Furthermore, Japanese Provisional Patent Publication No. 120626/1983 discloses an active energy ray curing composition a film of which is formed on the surface of a substrate by the irradiation of active energy rays such as ultraviolet rays, a main component of the composition being an urethane polyacrylate obtained by the reaction of a hydroxyl group-containing epoxy compound which contains an aromatic hydrocarbon group and an ether bond or contains an aromatic, an alicyclic or an aliphatic hydrocarbon group and an ester bond in its molecular and which has a hydroxyl group as a side chain and an epoxy ring at a chain end; a polyisocyanate; and a hydroxyl group-containing (meth)acrylate. Such a composition just mentioned has the advantage that a treatment can be carried out in the absence of any solvent, but the adhesion of this composition to the substrate is not satisfactory, since it is dependent upon an amount of unreacted epoxy groups. Particularly, such a composition has the fault that its heat-resistant adhesion to the glass plate is poor.